In the photo process, the glass substrate is coated with photo resistance by the glue spreader and enters into the exposure apparatus for exposure, so that the area covered by the photo resistance in the glass substrate may form a photo resistance image. In practice, if a foreign matter exists on the carrier of the exposure apparatus, a partial upheaval may occur on the glass substrate where the foreign matter lies and thus lead to a partial offset in the photo resistance image, thereby reducing the yield of the glass substrates achieved by photoetching in the photo process.
The foreign matter on the carrier of the exposure apparatus is commonly formed by the dropped debris from the abrasion of the bearing for the lifter in the exposure apparatus. Since the lifter is often manually operated, whether the bearing is abraded is determined according to hand feeling. However, it is easy to get a false determination and low checking efficiency, thereby significantly reducing the production efficiency of the photo process.